This invention relates to a novel promoter, a novel DNA construct containing the promoter and a Bt gene, and plants, especially corn plants, containing the novel DNA construct.
Bacillus thuringiensis (Bt) belongs to a large group of gram-positive, aerobic, endospore forming bacteria. During sporulation, these specific bacteria produce a parasporal inclusion body which is composed of insecticidally active crystalline protoxins, also referred to as .delta.-endotoxins.
These endotoxins are responsible for the toxicity of Bacillus thuringiensis to insects. The endotoxins of the various Bacillus thuringiensis strains are characterized by high specificity with respect to target organisms. With the introduction of genetic engineering it has become possible to create recombinant Bt strains which may contain a chosen array of insect toxin genes, thereby enhancing the degree of insecticidal activity against a particular insect pest.
The insecticidal crystal proteins from Bt have been classified based upon their spectrum of activity and sequence similarity (Hofte and Whiteley, Microbiol. Rev., 1989, 53:242-255 and Yamamoto and Powell, Advanced Engineered Pesticides, 1993, 3-42). Hofte and Whiteley published a classification scheme for the cry genes. Type I genes were considered active only against Lepidoptera species; Type II genes were active against Lepidoptera and Diptera species; Type III genes were active against Coleoptera species and Type IV genes included both 70- and 130-kDa crystal protein and were highly active against mosquito and blackfly larvae. However, since this original classification many novel cry genes have been cloned and sequenced demonstrating that the original system based on insect specificity required modification. A classification based on sequence homology along with new nomenclature based solely on amino acid identity has been proposed. (See Crickmore et al., Abstracts 28th Ann. Meeting Soc. Invert. Path. (1995), p14, Soc. Invert. Path., Bethesda Md).
In this invention, the Cry proteins which are particularly effective against Lepidoptera species are preferred. These proteins are encoded by the following nonlimiting group of genes: cry1Aa, cry1Ab, cry1Ac, cry1B, cry1C, cry1D, cry1E, cry1F, cry1G, cry2A, cry9C, cry5 and fusion proteins thereof. Among the cry genes, cry1Aa, cry1Ab, and cry1Ac show more than 80% amino acid identity and cry1Ab appears to be one of the most widely distributed cry genes. The Cry1Ab proteins are particularly effective against larvae of Lepidoptera (moths and butterflies).
The ingestion of these proteins, and in some cases the spores, by the target insect is a prerequisite for insecticidal activity. The proteins are solubilized in the alkaline conditions of the insect gut and proteolytically cleaved to form core fragments which are toxic to the insect. The core fragment specifically damages the cells of the midgut lining, affecting the osmotic balance. The cells swell and lyse, leading to eventual death of the insect.
A specific Lepidoptera insect, Ostrinia nubilalis (European corn borer (ECB)), causes significant yearly decrease in corn yield in North America. One study reveales that approximately 10% of the corn acres planted in the State of Illinois experienced a 9 to 15 percent annual yield loss, attributable solely to damage caused by the second generation of corn borer. Other important lepidopteran insect pests of corn include Diatraea grandiosella (Southwestern Corn Borer), Helicoverpa zea (Corn Earworm) and Spodoptera frugiperda (Fall Armyworm). The management practices of planting resistant or tolerant corn hybrids and treatment with chemical and microbial insecticides have not been satisfactory due to the low level of control provided by insecticidal treatments and the lack of hybrid lines resistant to second generation corn borers. Further tolerant and resistant hybrids often do not yield as well when infestation of ECBs are heavy. The use of corn genetically engineered to be resistant to specific corn insect pests has many advantages and these include a potential for substantial reduction in chemical insecticides and selective activity of the engineered endotoxin which will not disrupt the population of beneficial non-target insect and animals.
Toxic Bt genes from several subspecies of Bt have been cloned and recombinant clones have been found to be toxic to lepidopteran, dipteran and coleopteran insect larvae. However, in general, the expression of full length lepidopteran specific Bt genes has been less than satisfactory in transgenic plants (Vaeck et al, 1987 and Barton et al, 1987). It has been reported that the truncated gene from Bt kurstaki may lead to a higher frequency of insecticidal control. (U.S. Pat. No. 5,500,365). Modification of the existing coding sequence by inclusion of plant preferred codons including removal of ATTTA sequences and polyadenylation signals has increased expression of the toxin proteins in plants. (U.S. Pat. No. 5,500,365). In the present invention a truncated Bt kurstaki HD-1 gene has been used.
The instant invention additionally includes a second coding segment. The second coding segment comprises a DNA sequence encoding a selective marker for example, antibiotic or herbicide resistance including cat (chloramphenicol acetyl transferase), npt II (neomycin phosphototransferase II), PAT (phosphinothricin acetyltransferase), ALS (acetolactate synthetase), EPSPS (5-enolpyruvyl-shikimate-3-phosphate synthase), and bxn (bromoxynil-specific nitrilase). A preferred marker sequence is a DNA sequence encoding a selective marker for herbicide resistance and most particularly a protein having enzymatic activity capable of inactivating or neutralizing herbicidal inhibitors of glutamine synthetase. The non-selective herbicide known as glufosinate (BASTA.RTM. or LIBERTY.RTM.) is an inhibitor of the enzyme glutamine synthetase. It has been found that naturally occurring genes or synthetic genes can encode the enzyme phosphinothricin acetyl transferase (PAT) responsible for the inactivation of the herbicide. Such genes have been isolated from Streptomyces. These genes including those that have been isolated or synthesized are also frequently referred to as bar genes. As used herein the terms "bar gene" and "pat gene" are used interchangeably. These genes have been cloned and modified for transformation and expression in plants (EPA 469 273 and U.S. Pat. No. 5,561,236). Through the incorporation of the pat gene, corn plants and their offspring can become resistant against phosphinothricin (glufosinate).